1. Field of the Invention
The present invention relates to an abrasive for polishing and, more particularly, to an SiO2/Al2O3 composite abrasive. The present invention also relates to a method for producing the composite abrasive.
2. Related Prior Art
As an important material for polishing, Al2O3 abrasives can be applied to the surface treatments of metal, glass, optical lens, compact disks etc. The Al2O3 abrasive usually provides high polishing rates to obtain a flat surface, however, the roughness increases as well. One way to solve such a problem is to modify the Al2O3 abrasive into a composite material by mixing with other materials. Additionally, for conventional Al2O3 abrasives, the polishing slurry has to be maintained at a low pH value, usually about 4, so that the Al2O3 abrasives can be well dispersed in water.
U.S. Pat. No. 6,261,476 mentioned a method to promote the polishing effect by simply blending abrasives of different sizes, which is adopted for chemical mechanical polishing (CMP) by most users now.
Mutsuo Sando, et al. mentioned another method in Funtai Kogaku Kaishi (1992, 29(10), 755-761), in which an SiO2 layer is provided on an xcex1-Al2O3 abrasive surfaces. Unfortunately, the surface potential of this composite abrasive drops instantly when the pH value of the solution is higher than 5. That is, such composite material cannot be used in high-pH solutions.
Therefore, it is desirable to provide an improved polishing abrasive to mitigate and/or obviate the aforementioned problems.
An object of the present invention is to provide a modified SiO2/Al2O3 composite abrasive, which has positive surface charges when dispersed in an alkaline solution.
Another object of the present invention is to provide a method for producing the modified SiO2/Al2O3 composite abrasive.
The modified SiO2/Al2O3 composite abrasive of the present invention can be used for polishing in an alkaline solution because of the positive surface charges, and exhibits good polishing rates because of the Al2O3 cores. The SiO2 layer coated on the Al2O3 core usually has a thickness ranging from 1 nm to 100 nm.
The method for producing the SiO2/Al2O3 composite abrasive of the present invention is to mix an Al2O3 abrasive and a precursory material in an alcohol. The mixture is then reacted with an acidic solution.
The precursory material aforementioned can be a silicide with an alkoxy group, for example, tetraethoxysilane. The alcohol can be C1-4 alkyl alcohol, preferably isopropanol. The acidic solution can be inorganic, for example, sulfuric acid and hydrochloric acid; or organic, for example, acetic acid.